Many menopausal women experience interrupted sleep due to frequent hot flashes that awaken them several times during the night. Hot flashes can continue for many years postmenopausally, posing a problem of considerable magnitude for millions of women. More women seek medical help for hot flashes than for any other menopausal problem. Anecdotally, women report that cool temperature reduces the frequency or intensity of their hot flashes. We have demonstrated that daytime hot flashes are suppressed by a cool ambient temperature (Ta). We now propose to extend this work to determine whether cool Tas can improve sleep by inhibiting nocturnal hot flashes or altering sleep characteristics. The object of the proposed research is to study the relationships between thermoregulatory variables, hot flashes, and sleep. Ambient temperature, sleep, hot flashes, and body temperature: The effect of ambient temperature on the frequency and intensity of hot flashes, on sleep characteristics and on body temperature will be examined by exposing menopausal women who have never had hot flashes, and those with frequent hot flashes to neutral and cool ambient temperatures for 24 hour periods, during which time sleep and thermophysiological variables (heart rate, skin resistance, skin and core temperatures, and sensation) will be measured. Arousal state, Ta and hot flash pattern: Distribution of hot flashes across sleep stages will be tabulated to determine whether and how sleep may influence hot flash patterns. The information provided by this research will further our understanding of hot flashes and of the interactions between thermoregulation and sleep. In addition, recommendations of appropriate ambient temperature regimens may offer an effective alternative to pharmacological treatment for the HFs and sleep disturbances of menopausal women.